Hello,
While I was investigating potential SYN flooding warning messages on my Linux
box for our DNS traffic,I was very surprised to see the backlog was set to very
small numbers for BIND tcp sockets.
strace showed backlog was '10' for listening socket for port 53 and '128' for
listening socket for port 953 (rdnc traffic).
I've restarted BIND after I updated somaxconn but BIND didn't pick up the value.
Why doesn't BIND set the backlog to a huge number and let OSes reduce it to
whatever somaxconn is? Or just set backlog to whatever is is set for somaxconn?
[x@h1:~ 21:11:49]$ sysctl net.core.somaxconnnet.core.somaxconn = 16384
[x@h1:~ 21:10:40]$ grep -C 2 -w listen
bind.strace*bind.strace.6692-setsockopt(20, SOL_SOCKET, SO_REUSEADDR, [1], 4) =
0bind.strace.6692-bind(20, {sa_family=AF_INET6, sin6_port=htons(53),
inet_pton(AF_INET6, "::", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) =
0bind.strace.6692:listen(20, 10) =
0bind.strace.6692-mprotect(0x7ff1c81bb000, 32768, PROT_READ|PROT_WRITE) =
0bind.strace.6692-mprotect(0x7ff1c81c3000, 12288, PROT_READ|PROT_WRITE) =
0--bind.strace.6692-setsockopt(21, SOL_SOCKET, SO_REUSEADDR, [1], 4) =
0bind.strace.6692-bind(21, {sa_family=AF_INET, sin_port=htons(53),
sin_addr=inet_addr("127.0.0.1")}, 16) = 0bind.strace.6692:listen(21, 10)
= 0bind.strace.6692-mprotect(0x7ff1c82a6000, 36864,
PROT_READ|PROT_WRITE) = 0bind.strace.6692-mprotect(0x7ff1c82af000, 8192,
PROT_READ|PROT_WRITE) = 0--bind.strace.6692-setsockopt(22, SOL_SOCKET,
SO_REUSEADDR, [1], 4) = 0bind.strace.6692-bind(22, {sa_family=AF_INET,
sin_port=htons(53), sin_addr=inet_addr("10.89.9.126")}, 16) =
0bind.strace.6692:listen(22, 10) =
0bind.strace.6692-mprotect(0x7ff1c8391000, 36864, PROT_READ|PROT_WRITE) =
0bind.strace.6692-mprotect(0x7ff1c839a000, 8192, PROT_READ|PROT_WRITE) =
0--bind.strace.6692-setsockopt(23, SOL_SOCKET, SO_REUSEADDR, [1], 4) =
0bind.strace.6692-bind(23, {sa_family=AF_INET, sin_port=htons(953),
sin_addr=inet_addr("127.0.0.1")}, 16) = 0bind.strace.6692:listen(23, 128)
= 0bind.strace.6692-write(7, "\27\0\0\0\375\377\377\377", 8)
= 8bind.strace.6692-mprotect(0x7ff1bf627000, 8192,
PROT_READ|PROT_WRITE) = 0--bind.strace.6692-setsockopt(24, SOL_SOCKET,
SO_REUSEADDR, [1], 4) = 0bind.strace.6692-bind(24, {sa_family=AF_INET6,
sin6_port=htons(953), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0,
sin6_scope_id=0}, 28) = 0bind.strace.6692:listen(24, 128)
= 0bind.strace.6692-write(7, "\30\0\0\0\375\377\377\377", 8) =
8bind.strace.6692-gettimeofday({1413483241, 939723}, NULL) = 0
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